Fix keyboard access and names for core controls

[byot-dot]

Summary

This fixes a small set of high-impact accessibility problems in shared/global controls:

• makes the connected wallet trigger a native button instead of a click-only div
• exposes the wallet popover's expanded state
• makes clickable balances native buttons so they are keyboard operable
• adds accessible names to the mobile navigation, toast-dismiss, and settings icon buttons
• exposes the mobile navigation relationship and expanded state with aria-controls / aria-expanded

These address keyboard and control-semantics issues under WCAG 2.2, primarily 2.1.1 (Keyboard) and 4.1.2 (Name, Role, Value).

The changes are intentionally narrow and preserve the existing visual behavior.

I found additional accessibility issues while reviewing the dashboard, including form labeling, standalone dialog behavior, chart alternatives, and contrast. If continued accessibility cleanup would be useful, I'm happy to keep working through them in similarly small, reviewable PRs.